The Types of Injuries

Muscle strains usually happen while a muscle is working as a brake—lengthening under load, like a sprinter's hamstring slowing the swinging leg. Most occur where muscle turns into tendon. Grade I hurts but barely limits you; grade II limits movement and strength with swelling; grade III is a major tear with marked loss of function. Bruising suggests grade II–III. Squeezing or stretching the muscle reproduces the pain, and weakness is the main problem.

Fascia is the sleeve of connective tissue wrapped around muscles—like a sausage casing that also stores energy. It is often injured with the muscle and feels the same, so it is rehabbed the same way.

Tendons connect muscle to bone. Most tendon problems come from doing too much, too often—high volume of low forces—causing tendinopathy (not true inflammation, so "tendinitis" is outdated). Pain sits on the tendon near the joint, not in the muscle belly, with no bruising. It is often worse when cold and eases as you warm up, and it hurts when you squeeze the muscle, stretch it or compress the tendon. A sudden pop with inability to use the muscle (for example, no calf raise) suggests rupture.

Ligaments hold bone to bone and guide joints—you cannot squeeze them. They are hurt by twisting or over-stretching (an ACL while pivoting) or by build-up of small stresses (a pitcher's elbow ligament). Grade I: pain, joint stable. Grade II: more pain, swelling inside the joint, some looseness. Grade III: full tear, obvious instability. Pain comes from moving the joint in the injury direction, not from squeezing a muscle.

The capsule is a balloon around the joint that holds joint fluid, so swelling stays inside the joint. It is usually injured along with ligaments and cartilage—for example in a shoulder dislocation.

Fibrocartilage forms the meniscus, the hip and shoulder labrum and spinal discs; hyaline cartilage covers bone ends. Traumatic injuries happen in one moment (a dislocation tearing the labrum, a heavy lift bulging a disc). Degenerative changes build up over years and are a normal part of ageing. Moderate activity keeps cartilage healthy; too little or too much can wear it faster. Torn cartilage can cause catching, locking or instability.

Nerves can be stretched, compressed or cut. A "pinched nerve" is usually inflamed rather than actually pinched—most disc bulges never touch the nerve. Symptoms (tingling, numbness, burning, shooting pain) follow the nerve's path and worsen the longer a position is held. Symptoms moving further down the limb (peripheralisation) mean things are worsening; moving back toward the spine (centralisation) means healing.

Bones can break by bending, compression, pulling apart, twisting or repeated loading (stress fracture). Major fractures are usually obvious—a snap, deformity, severe pain and swelling. A stress fracture gives sharp pain on one spot of bone that hurts to press and to load. Bone heals well because it has good blood supply.